32 RALPH S. LILLIE 



Three types of artificial membrane-forming treatment were 

 employed: (1) exposure for five minutes to pure isotonic sodium 

 chloride solution (0.55m. NaCl); (2) exposure for one to two 

 minutes to a weak solution of a fatty acid (acetic or butyric) 

 in sea-water; and (3) exposure to warm sea-water (at 35°) for 

 seventy seconds. 



In the majority of experiments the eggs were thus treated at 

 about the time of separation of the first polar body — ^that is, 

 from one to one-and-a-quarter hours after removal from the ani- 

 mals — this being the time at which the eggs respond most fa- 

 vorably to either normal or p^rthenogenetic fertilization. In a 

 number of instances the same treatment was applied also after 

 maturation was complete, at three to four hours after removal. 

 Of eggs treated at this time the proportion reaching larval stages 

 is typically much smaller than in the first class of cases; this de- 

 crease in responsiveness to artificial treatment is probably cor- 

 related with the decreased susceptibility to sperm-fertilization 

 which appears at this time;^^ the unfertilized eggs seem then 

 normally to enter on a refractory or relatively irresponsive phase 

 in the life-cycle. In several series of experiments, however, de- 

 velopment proved more favorable in eggs which were treated 

 after maturation was complete; this occurred chiefly in abnormal 

 lots of eggs which exhibited delay in the post-maturational cy- 

 tolysis and imperfect development after sperm-fertilization. In 

 all those experiments where eggs treated two or three hours after 

 maturation formed a considerable proportion of larvae (10-20 per 

 cent), sodium chloride solution was the membrane-forming agent; 

 this solution appears to act more energetically than the other two 

 agents and is possibly for this reason better able to overcome the 

 increased resistance which the eggs show at this stage. 



The experiments with each of the above types of membrane- 

 forming treatment will now be described separately in some 

 detail. 



R. S. Lillie, Journal of Experimental Zoology, 1908, vol. 5, p. 411. 



